Study On The Permeability And Characteristics Of The Groundwater Quality Of Coral Reef

On the islands far from the mainland,the underground water surface has a certain amount of fresh water resources due to rainfall infiltration with its distributed in the middle thickness and thin on both sides.This fresh water resources is an important resource and guarantee for producting the living of the islanders and the island ecosystem.In this paper,study on such a coral reef with the change regular of groundwater.The seepage characteristics with the horizontal and vertical of calcareous sand were grasped via double ring osmosis test and pumping test.It provides theoretical basis for infiltration law to rainfall and determines the nature of the soil layer combined speccific yield.We selected the open calcareous sand on a calcareous sand island,and buried sensors of soil conductivity,volumetric water content and temperature at the depth of 0.5m,1.0m,1.5m to monitor the calcareous sand conductivity and volumetric water content.Selected three specific representative areas to drilling deep hole,and placed sensors of conductivity,waterlevel and temperature at different depth to monitor the change of conductivity.Meanwhile,to observe the change of chloride ion concentration for different periods of time by Matan2 sensor.The main conclusions are as follows:(1)The experiment of double ring penetration and indoor density experiment showed the permeability coefficient of calcareous sand becomes negative correlation with density,compactness and nonuniformity coefficient Cu,and becomes,positive correlation with d4/d60n via referencing "crushing particle size"d4.The n takes 2,5,4,3 according to the rand of the coefficient of heterogeneity is Cu?5,5<Cu?10,10<Cu?20 and Cu?20.Then to deduce the formula of permeability coefficient of calcareous sand.(2)It carried out the pumping test included two depth with three drawdown.On the about 18 meters of the surface,its permeability coefficient is about lm/d.And its specific yield of the two depth is 5.08%and 20.88%.And then judging that the calcareous sandy soil layer is mainly composed of fine sand.(3)Calcareous sand conductivity becomes positive correlation with volatile water content.They meet ECb=??ECw+ECs in the case of low volume water content.a relatives to porosity and takes 0.8?1.3 in full saturation.The porosity is more smaller and a is more smaller.The intercept of this formula is not zero to reflecting electrical conductivity on the particle surface.(4)Ignoring evaporation,the one-dimensional model of the relationship between calcium sand conductivity and the rainfall and its depth was obtained by analyzing the data of three parameters of soil and the rainfall combined infiltration law to rainfall.(5)It not considers the rised capillary because it exists evaporation about 40cm deep soil via evaporation experiments on site.The vertical hydraulic conductivity is greater than-that of horizontal less than 7 meters in the soil,but it is opposite over 7 meters in the soil.The chloride ion concentration for one year combined Seepage field and specific yield shows that dilute region is the "pouring bowl" characteristic in the center of the reef by building a three-dimensional map in Voxler software.That is same thickness into the bowl with bottom up,and it presents brim type towarded horizontal direction after reaching a certain depth.